If it's something simple, it's easy and the best thing is to do it again. If it's something complex it will not get a good result by decompiling the code. In any case the best result is to do it again, take advantage to learn a little more and take more care next time. Decompilation does not produce a good result so it can be handled properly.
But if you want to insist you have a question that shows you some options to see the IL code and also generate the code in C #. Some work better than others.
If you are thinking about doing this in third-party codes, think twice, you may be committing some illegal.